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Tissues and the Primary Growth of Stems, image, image, corms, bulbs,…

- - - - fibers are long and strong, resist insects fungi and pests
        
        agave fibers
      - sclereids are short and cuboidal and become hard and brittle, like shells of walnuts or stones of cherries and peaches
      - secondary cells walls become impregnated with lignin, making them waterproof
    - - tracheids - long and narrow with tapered ends, not perforated, dead at maturity, found in all vascular plants
      - vessel elements - short and wide with perpendicular end walls, dead at maturity, found exclusively in flowering plants - a few ferns, horsetails, and gymnosperms have vessels
      - moves water
- - - - conducts water and minerals
      - tracheids
      - vessel elements
      - tracheary elements are formed from parenchyma cells that develop a secondary wall then die and become hollow
      - circular bands of secondary walls are called annular thickenings
      - helical thickening has one to three helices interior to primary wall
      - scalariform secondary wall underlies most of the primary wall
      - reticulate thickening is in the shape of a net
      - pits are gaps where the secondary wall is absent and allow the flow of water but are weak and require a border
      - circular bordered pits are the most derived and strongest
      - lamella between pits of primary walls has a pit membrane
      - perforations are digested in one of the cell walls to allow water to pass
      - a stack of vessel elements creates a vessel
    - - distributes sugar and minerals
      - two types of cells, sieve and sieve tube members, seive elements refers to both
      - unlike the xylem cells, these parenchyma stay alive and have one cell wall
      - as they differentiate into sieve elements their plasmodesmata enlarge allowing bulk movement from cell to cell
      - sieve cell with sieve area
        
        long narrow, with ends pointed sieves are small and located all over the cell surface, all nonangiosperm vascular plants
        
        associated with albuminous cells
      - sieve tube member
        
        short/wide with flat ends, small sieves on side walls, large sieve plate on end wall
        
        controlled by companion cells
    - - these are just interior to the cortex
      - collateral - contains both xylem and phloem
      - vascular bundles occur in a ring around the pith, a parenchyma layer